(a) Field of the Invention
The present invention relates to an organic electroluminescent device having an excellent luminance property such as high luminance efficiency.
(b) Description of the Related Art
An organic electroluminescent device (which will hereinafter be called xe2x80x9corganic EL devicexe2x80x9d) is a light-emitting device which makes use of the principle that when an electric field is applied, a fluorescent material emits light in response to the charge recombination of holes injected from an anode and electrons injected from a cathode. After C. W. Tang et al. of Eastman Kodak Company reported a low-voltage-driven organic EL device using a double layered structure (C. W. Tang, S. A. Vanslyke, Applied Physics Letters, Vol. 51, 913 (1987) and the like), studies on an organic EL device have been briskly carried out. Tang et al. reported an organic EL device using tris(8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative in a hole-transporting layer. This stacked structure gives such advantages as an improvement in the injection efficiency of holes into the light-emitting layer; and confinement of the excitons into the light-emitting layer. A double layered structure composed of a hole-injecting and transporting layer and an electron-transporting and light-emitting layer or a triple layered structure composed of a hole-injecting and transporting layer, a light-emitting layer and an electron-injecting and transporting layer is well known as an organic EL device. In order to increase the recombination efficiency of injected holes and electrons, various improvements in the device structure or fabrication process have been introduced to such multi-layered devices.
As a hole transporting material, triphenyl amine derivatives and aromatic diamine derivatives such as 4,4xe2x80x2, 4xe2x80x3-tris(3-methylphenylphenylamino)-triphenyl amine which is a star burst molecule and N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamine are well known (for example, Patent Publications JP-A-8-20771, JP-A-8-40995, JP-A-8-40997, JP-A-8-53397, and JP-A-8-87122). As an electron transporting material, oxadiazole derivatives, triazole derivatives and the like are well known.
Chelate complexes such as tris(8-quinolinolate)aluminum complex, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, oxadiazole derivatives and the like are known as light emitting materials. Since various color lights in a visible region from blue to red are obtained from these light-emitting materials, there is increased expectation for industrialization of a full color organic EL device (refer to, e.g., JP-A-8-239655, JP-A-7-138561, and JP-A-3-200289).
In recent days, organic EL devices with high brightness and long lifetime have been disclosed or reported, but these are not yet sufficient.
It is therefore an object of the present invention to provide materials for the organic EL devices having high luminance.
The inventors have found as a result of diligent investigation for overcoming the above problems that an organic EL device having a specific one of pentacene compounds and of dibenzoperylene compounds as a luminescent material has much higher luminance than a conventional EL device. The material has been found to have a high carrier transporting ability, and an organic EL device prepared by employing the above material as a hole transporting material or an electron transporting material and another organic EL device prepared by employing a mixed thin film comprising the material and another hole transporting material or electron transporting material has been found to have higher luminance than the conventional one.
It has been also found that an organic EL device prepared by employing, as a luminescent material, a hole transporting material or an electron transporting material, a pentacene compound and/or a dibenzoperylene compound, among the above pentacene and dibenzoperylene compounds, having a diarylamino group as a substituent exhibits an especially high luminance. It has been also found that an organic EL device prepared by employing, as a luminescent material, a hole transporting material or an electron transporting material, a pentacene compound and/or a dibenzoperylene compound, among the above pentacene and dibenzoperylene compounds, having a styryl group as an aryl group exhibits an especially high luminance. The present invention is based on these findings.
Thus, the present invention provides, in a first aspect thereof, an organic electroluminescent device comprising an anode, a cathode, and one or more organic thin film layers disposed between said anode and said cathode, at least one of said layers containing, in a form of a mixture or a single substance, a pentacene compound expressed in Formula 1. 
Wherein each of R1 to R14 independently represents a hydrogen atom, a halogen atom, a hydroxyl group, a substituted or non-substituted amino group, nitro group or cyano group, a substituted or non-substituted alkyl group, a substituted or non-substituted alkenyl group, a substituted or non-substituted cycloalkyl group, a substituted or non-substituted alkoxyl group, a substituted or non-substituted aromatic hydrocarbon group, a substituted or non-substituted aromatic heterocyclic group, a substituted or non-substituted aralkyl group, a substituted or non-substituted aryloxy group, a substituted or non-substituted alkoxylcarbonyl group, or a carboxyl group. The substituents R1 to R14 may form a ring between two of them. At least one of R1 to R14 is a diarylamino group expressed by xe2x80x94NAr1Ar2 (each of Ar1 and Ar2 independently represents a substituted or non-substituted aryl group having 6 to 20 carbons, and at least one of these has a styryl group expressed in Formula 2 below and a ring may be formed between two of them. 
Wherein each of R15 to R25 independently represents a hydrogen atom, a halogen atom, a hydroxyl group, a substituted or non-substituted amino group, nitro group- or cyano group, a substituted or non-substituted alkyl group, a substituted or non-substituted alkenyl group, a substituted or non-substituted cycloalkyl group, a substituted or non-substituted alkoxyl group, a substituted or non-substituted aromatic hydrocarbon group, a substituted or non-substituted aromatic heterocyclic group, a substituted or non-substituted aralkyl group, a substituted or non-substituted aryloxy group, a substituted or non-substituted alkoxylcarbonyl group, or a carboxyl group. The substituents R15 to R25 may form a ring between two of them.
The present invention further provides, in a second aspect thereof, an organic electroluminescent device employing a compound expressed in Formula 3 in place of that expressed in Formula 1 of the first aspects.
The present invention further provides, in a third aspect thereof, an organic electroluminescent device employing a compound expressed in Formula 4 in place of that expressed in Formula 1 of the first aspect. 
In accordance with the present invention, the organic EL device effectively exhibits higher luminance than that obtained by a conventional organic EL device by employing the specified pentacene or dibenzopeylene compound.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.